This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 6 |
| 5 | 18 |
| 6 | 57 |
| 7 | 168 |
| 8 | 504 |
| 9 | 1515 |
| 10 | 4542 |
| 11 | 13626 |
| 12 | 40881 |
| 13 | 122640 |
| 14 | 367920 |
| 15 | 1103763 |
| 16 | 3311286 |
| 17 | 9933858 |
| 18 | 29801577 |
| 19 | 89404728 |
| 20 | 268214184 |
| 21 | 804642555 |
| 22 | 2413927662 |
| 23 | 7241782986 |
| 24 | 21725348961 |
| 25 | 65176046880 |
| 26 | 195528140640 |
| 27 | 586584421923 |
| 28 | 1759753265766 |
| 29 | 5279259797298 |